This invention relates to a rotary heat sealing method and apparatus for the high speed continuous motion heat sealing in the transverse direction of a moving, multiple layer web of thermoplastic film.
The method and apparatus of the present invention is particularly suited for the manufacture of drawtape bags where the bags and the drawtapes are made of thermoplastic material such as for example polyethylene film. Examples of such draw tape bags are disclosed in U.S. Pat. Nos. 4,597,750 and 4,624,654. In the manufacture of draw tape bags, the ends of the drawtapes are presealed to the multiple layer web of film at the areas where the side seals of the bags are to be made to insure that the drawtapes will not pull loose from the side seals. It has been the practice heretofore to make the preseal by stopping the web and pressing heated seal bars against the preseal area. Other examples of heat sealing apparatus for plastic webbing are disclosed in U.S. Pat. Nos. 3,221,613 and 3,466,979. In U.S. Pat. No. 2,125,758 only instantaneous contact is made between the web and the heated roll.
It is an object of the present invention to provide a method and apparatus of accomplishing a preseal in a continuous manner without stopping the web and without the reciprocating motion of the seal bars, thus permitting a much higher speed of operation.